let str = 'str'

//union types
let numberOrString: number | string
numberOrString.toString()

function getLength (input: string | number): number{
    const str = input as string
    if (str.length){
        return str.length
    }else{
        const number = input as number
        return number.toString().length
    }
}

//type guard
function getLength2 (input: string | number): number{
    if (typeof input === 'string'){
        return input.length
    }else {
        return input.toString().length
    }
}